Wave signaling system



L. A. HAZELTINE WAVE SIGNALING SYSTEM Original Filed Feb. 27, 1925louis/1H Awww INVENTQR azeZ m e f BY ATTORNEYS APatented Nov. 20, 1928.

,UNITED STATES PATENT. yoFFici-i.

LOUIS A. HAZELTINE, 0F HOBOKEN, NEW JERSEY, ASSIGNOR TO HAZELTINE COR-PORATION, A CORPORATION OF DELAWARE.

WAVE SIGNALING SYSTEM.

Original application filed/February 27, 1925, Serial `No 12,000PatentNo. 1,648,808, and in Canada May 4, 1925. Divided and this applicationfiled October 31, 1927. Serial No. 229,912.

This ,invention relates to wave signaling systems, particularly radioreceiving systems employing tuned radio-frequency amplification, and hasfor its object the provision of means for securing substantiallycomplete neutralization of the capacity coupling in vacuum tubes undercertain circumstances.

In my United States Letters Patent No. 1,533,858, granted April 14,1925, there are described means for eliminating coupling between stageskof an amplifier including the neutralization of the capacity couplingbetween the grid and plate electrodes of a vaclium tube and between theapparatus connected thereto. Such neutralization is accomplished,briefiy, by the use of an auxiliary coil and a neutralizing condenserconnected in series between the grid and the filament system, theneutralizing coil being coupled to a primary coil connected between theplate and the yfilament system.

In general for com-plete neutralization the coupling between theauxiliary coil and the primary coil should be so close as to behavepractically like perfect coupling-that, is, with a coupling coeflicientequall to unity. Now circumstances sometimes arise in which thecouplingby choice or necessity is looser, no longer behaving like perfectcoupling and so resulting inN incomplete neutralization. For example, atrelatively low frequencies itmay be desired to employ coils having theirturns bunclied or wound -in spiderweb form or mounted on individualsupporting structures, resulting in each case in a .physical separationof the coils. Again,` at very high frequencies the reactances of theleads become appreciable even lwhen the leads are made as short asfeasible, thus also loosening the coupling between the circuits of Ythecoils. In accordance with this invention it has been found thatsubstantially complete neutralization may be attained at all frequencieswithin frequency amplifying transforme-r the coils of which are arrangedin accordance. with this invention and suited for use in a lowradiofrequency amplifier such as represented in ydetector tube D, arethen amplified at the pulse frequency by A1 and A2 again, on the reflexprinciple, and are finallylamplified and supplied to the relay by thevacuum tube A,.. These and other details are more fully described in mcopending application for United States ette-rs Patent No. 12,000, filed/February 27, 1925, issued November 8, 1927,

present A y as Patent No. 1,648,808, of which this application isadivision.

Interstage radio-frequency couplings are minimized by thevuse ofindividual metal compartments for each stage and 'bythe use of seriesresistances Rp, Rg, or impedance Lpd, and shunt capacities Cp, Gg, Cp.,Cpd and Ca,

in the leads, and especiall by the neutralization mea-ns involving coi sL Lm, LS1, and condenser C, in one stage, and coils L2,'L2, L52, andcondenser (32 in the other stage.

The use for which the receiver of Fig. 1 is intendedinvolves relativelylow radio frequencies, where the single-layer type of secondary winding(commonly used in broadcast receivers) is preferably replaced by amultilayer coil Ls and where the primary coil L, and auxiliary coil Ln'may be of the pancake form, placed close together, as represented inFig. 2, where Ln, Lp, L, indicate either Lm, Lm', LS1, or LM, Lpg, Ls2of Fig. l. With this arrangement, as previously mentioned, it isdifficult to secure the exceedingly close coupling between lLrl and Lpwhich is desired. It hasbeen found, however, that ifthecouplingcoeiicient between Ln and the secondary'coil LS-is lequal tothe product of the coupling coeiiicienty between Ln and Lp, and the.

coupling coefficient between Lp and Ls, then the coeflicient of couplingbetween Ln and Lp need not be substantially unity. This result maybeattained with Lpplaced between Lnand ment of the respective vacuum tubeA, or

A2 being neutralized (allowing the filaments of the other vacuum tubesto remain lighted), to tune in a strong signal, and then to adjust theneutralizing capacity until the signal d1s appears. With close couplingbetween L., and Lp, the relation then existing would be C@ Nn -gf (l)where Cgp is the grid-plate coupling capacity,

Cn is the neutralizing capacity and Nn and Np l are the numbers of turnsof coils Ln and Lp, respectively, all for the stage being neutralized.If the coupling is not very close, the above procedure will result inthe existence of the following more generalrelation,

where Lns is the mutual inductance between Ln and LS, and Lps'is themutual inductance between Lp and Ls. Relation (2.) of course, reduces-torelation (l) for very close coupling, from the formula for mutualinductance, which for LnB and Lp, would have identical factors except Nnand Np, respectively.

Now when the filament is lighted, there will flow, in'addition to thecurrents previously present, the amplified plate current. This currentHows through coil Llp and gives rise to a self-induced voltage, in thatcoil proportional to the self-inductance Lp, and to y'a voltage in coilLn proportional `to/the mutual inductance Lm, between Ln and Lp. If abalance is still to be maintained, it is necessary that these voltagesproduce Vequal (and, of course, opposite) additional-currents through C@and Cn. Since the currents are proportional to the capacities, thelatter must be inversely proportional to the respective voltages. Hence-QLD- Ln CII- Lvl I Combining this relation with (2),

Now the coefficient of coupling k between two coils is defined as thequotient of the mutual Lesage? inductance by the square rootof theproduct of the self-inductances. Substituting this relation for eachmutual inductance in (4) we have 7cns'V LnLs: knp'JLnl- Jp 7c,1/LL Lpwhich at once reduces to the relation stated above enf/apa.. (6)

the conditionA (6), showing the advantage mentioned above of making thecoupling between Ln and L,D as close to unity as feasible.

The above derivation does not consider the voltages induced in theleakage self-inductances of Ln and Lp due to the capacity currentsflowing through them. However, the consideration of capacity current inLp leads to exactly the same result as above, since the derivation willapply to any current in Lp. The only error in neutralization thatremains is thus that due to the capacity current in the leakagereactance of Ln, this error manifesting itself by a slight theoreticalunbalance .at frequencies differing from that at which Cny is adjusted.Since the capacity associated with Ln, consisting of natural capacityplus C, is ordinarily very small, and the leakage self-inductance iskept; as small as feasible by fairly close coupling, this error can beshown to be ordinarily quite insignificant. The relations (2) and (6)therefore give substantially complete neutralization under all practicalconditions.

A suitable experimental procedure lfor atplete neutralization is asfollows: The filament of the vacuum tube to be neutralized is turned outand al strong signal is. impressed between its grid and filament. Theneutrali'zing capacity Cn and the coil couplings are then adjusted untilno signal voltage appears between the plate and the filament, both whenthe output circuit is tuned and when it is not. The absence of signalvoltage can conveniently be ascertained by a zero reading on a vacuumingtube voltmeter connected between the plate and filament system of thevacuum tube being neutralized. l

This invention is applicable to any amplifier in which the secondarycoil is connected in a closed alternating-current. circuit, whethertuned or not. If the circuit isvnot tuned, the procedure described inthe preceding paragraph is modified simply by obtaining a balance withat least two different impedance conditions in the secondary circuit, asfor example, open circuit and short circuit.

I claim:

l. In an electric circuit arrangement for neutralizing capacity couplingbetween the grid and plate circuits of a vacuum tube, including aprimary coil connected between the plate and the filament system, asecondary coil, andan auxiliary coil and a neutralizing capacityconnected in series between the grid and the filament system, theauxiliary and primary coils being utilized under such circumstances thatsubstantially unity coefficient of coupling between their circuits isnot present, the method of securing substantially completeneutralization, which comprises arranging said coils so that the ratioof the mutual inductance between the secondary coil and the auxiliarycoil to the mutual inductance between the secondary coil and the primarycoil is equal to the ratio of the mutual. inductance between theauxiliary coil and the primary coil to the self-inductance of theprimary coil and so that said ratios are also equal to the ratio of thecoupling capacity to the neutralizing capacity.

2. In an electric circuit arrangement for neutralizing capacity couplingbetween the grid and plate circuits of a vacuum tube, including a.primary coil connected between the plate and the filament system, asecondary coil, and an auxiliary coil and a neutralizing capacityconnected in series between the grid and the filament system, theauxiliary and primary coils being utilized under such circumstances thatsubstantially unity coeiiicient of coupling between their circuits isnot present, the method of securing substantially completeneutralization, irrespective of the currents flowing through the primaryand secondary coils, which includes the ste of interposing the primarycoil physically etween the other two coils in such manner that thecocoil, and an auxiliary coil and a neutralizing` capacity connected inseries between the grid and the filament system, the auxiliary andprimary coils being utilized under such circumstances that substantiallyunity coefficient of coupling between their circuits is not present, themethod of securing approximately complete neutralization, irrespectiveof the currents flowing through the primary and secondary coils, whichincludes the step of interposing the primary coil physically between theother two coils in such manner that the coefficient of coupling betweensaid other two l coils is less than the coefficient of coupling betweenthe primary and either of the other coils.

4. In an electric circuit arrangement for neutralizing capacity couplingbetween the grid and plate circuits of a vacuum tube, having a grid, a.plate, and a filament system, the combination of a secondary coil, anauxiliary coil, and a primary coil physically interposed between saidsecondary and auxiliary coils, whereby the coefficient of couplingbetween said secondary and auxiliar coils is less than the coeliicientof coupling etween said primary and either of the other coils saidprimary coil being connected between the plate and the filament system,said auxiliary coil being connected in series with a neutralizingAcapacity between the grid and said filament system, and said secondarycoil being connected in a closed alternating-current circuit.

In testimony whereof- I affix my signature.

LOUIS A. HAZELTINE.

